[libc++abi][NFC] Remove mentions of LIBCXXABI_SHARED_LIBRARIES

LIBCXXABI_SHARED_LIBRARIES doesn't exist anymore, so this always expanded
to nothing at all.

Author: ldionne

libcxxabi/src/CMakeLists.txt

@@ -168,7 +168,7 @@ if (LIBCXXABI_USE_LLVM_UNWINDER)
     target_link_libraries(cxxabi_shared_objects PUBLIC unwind_shared)
   endif()
 endif()
-target_link_libraries(cxxabi_shared_objects PRIVATE cxx-headers ${LIBCXXABI_BUILTINS_LIBRARY} ${LIBCXXABI_SHARED_LIBRARIES} ${LIBCXXABI_LIBRARIES})
+target_link_libraries(cxxabi_shared_objects PRIVATE cxx-headers ${LIBCXXABI_BUILTINS_LIBRARY} ${LIBCXXABI_LIBRARIES})
 target_link_libraries(cxxabi_shared_objects PUBLIC cxxabi-headers)
 set_target_properties(cxxabi_shared_objects
   PROPERTIES
@@ -204,7 +204,7 @@ if (LIBCXXABI_ENABLE_SHARED)
 
   target_link_libraries(cxxabi_shared
     PUBLIC cxxabi_shared_objects
-    PRIVATE ${LIBCXXABI_SHARED_LIBRARIES} ${LIBCXXABI_LIBRARIES})
+    PRIVATE ${LIBCXXABI_LIBRARIES})
 
   list(APPEND LIBCXXABI_BUILD_TARGETS "cxxabi_shared")
   if (LIBCXXABI_INSTALL_SHARED_LIBRARY)